1. Field of the Invention
The present invention relates to a combined wet etching method for stacked films and a wet etching system used in the combined wet etching method for stacked films and more particularly to the combined wet etching method for stacked films for performing wet etching processes employing a plurality of types of wet etching methods in combination and in a collective manner on stacked films containing a plurality of films each having a different film property.
The present application claims priority of Japanese Patent Application No. 2002-332954 filed on Nov. 15, 2002, which is hereby incorporated by reference.
2. Description of the Related Art
In processes of manufacturing liquid crystal display devices and semiconductor devices, in order to perform thin-film patterning, an etching process is indispensable. However, in wet etching processes to be performed on a thin film, so-called a “side-etching” phenomenon occurs, in which the thin film is excessively etched not only from a direction of a surface of the thin film but also from a direction of a portion surrounding the thin film, thus making it impossible to achieve a uniform shape of the thin film to be obtained after having been etched. In process for patterning a wiring layer by using a wet etching process to form wirings made of metal materials in particular, very high etching accuracy is required. This is because, if an irregularity occurs in a pattern shape due to insufficient accuracy in the side-etching, it exerts a large influence on electrical properties of devices.
Moreover, with recent widespread usage of multi-layered liquid crystal display devices and/or semiconductor devices, an influence of a step existing on a lower-layer pattern wielded over a step coverage characteristic of the lower-layer pattern by an upper-layer pattern becomes large. In an etching process for patterning wiring layers in particular, in order to maintain an excellent step coverage characteristic by an upper-layer pattern, to ensure an insulation pressure resistance of an interlayer dielectric being put between an upper-layer and a lower-layer, to achieve normal conduction through upper-layer metal wirings, and to obtain reliability by avoiding occurrence of a defect in a protective film covering upper-layer metal wirings, so-called a “taper etching” process, in which a tapered portion is formed on a surface being wet-etched at time of patterning on lower layer wirings, is an important factor.
To achieve this purpose, when a single wiring material (single layer) is wet-etched, in many cases, impregnation of an etching liquid between a resist and wiring material is used by making an adjustment to the chemical composition of the etching liquid or by controlling resist adhesion.
FIGS. 10A and 10B each are an outline of a general wet etching process conventionally employed. As shown in FIGS. 10A and FIG. 10B, in the conventional wet etching, after a substrate to be treated 1 has been carried into an etching chamber 2 by a substrate carrying roller 9, by performing an etching process 2a using a single method, that is, using wet etching such as immersion etching (static etching using a static etching liquid) in which the substrate is immersed in an etching liquid, or spray etching (dynamic etching using a dynamic etching liquid) in which an etching liquid is sprayed on a substrate, or a like, parts (specified regions) of a thin film formed on the substrate to be treated 1 are etched.
Next, after the substrate to be treated 1 has been carried into a water cleaning chamber 3, a cleaning process 3a, as shown in FIG. 10B, is performed to remove the etching liquid (etchant) being left on the substrate to be treated 1. Then, after the substrate to be treated 1 has been carried into a drying chamber 4, a drying process 4a is performed to remove cleaning water being left on the substrate to be treated 1. Thus, patterning is achieved by performing the wet etching process on the thin film. Moreover, a wet etching system using the conventional spray etching method as described above is disclosed in Japanese Patent Application Laid-open No. Sho 57-094572. Also, another conventional wet etching method employed for etching on a single-layered film in which the spray etching method and the immersion etching method are used in combination, however, each of the spray etching method and the immersion etching method is performed in etching systems being different from each other is disclosed in Japanese Patent Application Laid-open No. Hei 08-158069.
However, a following problem occurs when the conventional wet etching methods as described above are employed for etching on stacked films. That, there is a problem in that, when an etching process by using a same etching liquid is performed, in general, a etching characteristic (that is, etching rate) varies depending on each wiring material and in that, when an etching process by using a same etching liquid is performed on a same wiring material, a etching characteristic varies depending on an etching method to be employed.
Due to this, if an etching process is performed by a single method on a plurality of stacked wiring materials (stacked films) in the same manner employed in the etching on a single-layered film, if an etching rate of a lower layer film is larger than that of an upper layer film, which is caused by a difference in the etching rate of each of the stacked films, a side-etching phenomenon in the lower layer film excessively occurs compared with that in the upper layer film, causing occurrence of a overhanging shape of the upper layer film in which the upper layer film protrudes toward the lower layer film in a hood form in some cases. This overhanging shape of the upper layer causes degradation of a step coverage characteristic of a film to be further stacked on the upper layer, thus causing occurrence of structural defects in the upper layer film.
In order to eradicate such the difference in an etching rate which varies depending on a wiring material, an etching method may be available in which formation of a tapered portion is controlled by using two kinds of etching liquids each having a different etching characteristic. However, due to deterioration in each of the etching liquids and/or due to complicated management of concentrations of the etching liquids, actual operations of this etching method is not easy.